Depends how long you’ll be riding in the dark along with a bit of trial and error to see what works for you.
I went for the beema as-2000 on the bars and fluxient 1xU2 for the helmet – very similar to your setup, however the beema comes with an excellent battery as standard (7800mah).
I got an extra 7800mah battery too.
I then ran the helmet light on one of the large batteries, leaving me a 7800mah + 4400mah for the bar light. This gave me enough to run the helmet light on low setting all night long (15hrs) and the bar light on low for climbing and medium for descending.
I chose that way round because a lot of the relentless descent is narrow/rocky/twisty, so i valued a stronger flood in front of the front wheel. If the descents had been smoother and faster i may have used the extra battery for the helmet light.
If you are doing a summer 24hr then obviously you can run longer on higher modes, or with lower capacity batteries.